The present invention relates in general to magnetic field sensors and, more particularly, to a magnetic field sensor with split collector contacts for high sensitivity operation.
Magnetic field sensors are commonly used to detect the presence and orientation of a magnetic field. A magnetic field sensor may be formed in a semiconductor material, for example, as two lateral NPN bipolar transistors with separate collector regions, and a common base region, and a common emitter region, otherwise known as a magnetotransistor.
The principal of operation follows the Lorentz Force action on the movement of charge carriers (electrons for NPN transistors) in the semiconductor material. The Lorentz Force action on electrons is described by the equation F=-ev.times.B, and for holes by F=ev.times.B, where "e" is the electron charge, v is the velocity vector of the carriers, B is the magnetic induction vector, and F is the deflection force vector operating on the charge carriers due to the magnetic field. The bipolar transistors are biased in their forward active region of operation. In the absence of a magnetic field, a bias potential applied at the common base causes equal currents to flow through the collectors of the two lateral NPN transistors due to their symmetrical construction. When the magnetic field is applied parallel to the surface of the devices, the carriers deflect toward one collector according to the orientation of the magnetic field, thereby creating an imbalance between the collector currents of the bipolar transistors. The collector current imbalance is used to determine the strength and orientation of the magnetic field.
The separate collector regions of the bipolar transistors are susceptible to noise in the same way as the collector of a single bipolar transistor. Furthermore, the noise of the differential lateral transistors is higher than the noise of a single collector lateral transistor because the signals of the two separate collectors are not correlated. The noise presence limits the sensitivity of the magnetotransistor to the magnetic field. Therefore, a need exists for a magnetic field sensor with reduced effect from the noise for higher sensitivity.